目录
1. 整体学习的思维导图
2. 回顾基本查询
使用scott数据库中的表，完成以下查询：
-
查询工资高于500或岗位为MANAGER的雇员，同时还要满足他们的姓名首字母为大写的J
mysql> select * from emp where (sal>500 or job='MANAGER') and ename like'J%';
+--------+-------+---------+------+---------------------+---------+------+--------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno |
+--------+-------+---------+------+---------------------+---------+------+--------+
| 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 |
| 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 |
+--------+-------+---------+------+---------------------+---------+------+--------+-
按照部门号升序而雇员的工资降序排序
mysql> select * from emp order by deptno asc, sal desc; +--------+--------+-----------+------+---------------------+---------+---------+--------+ | empno | ename | job | mgr | hiredate | sal | comm | deptno | +--------+--------+-----------+------+---------------------+---------+---------+--------+ | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | +--------+--------+-----------+------+---------------------+---------+---------+--------+ -
使用年薪进行降序排序
mysql> select *,sal*12+ifnull(comm,0) 年薪 from emp order by 年薪 desc;
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno | 年薪 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+
| 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | 60000.00 |
| 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | 36000.00 |
| 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | 36000.00 |
| 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | 35700.00 |
| 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | 34200.00 |
| 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | 29400.00 |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 19500.00 |
| 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | 18000.00 |
| 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | 16400.00 |
| 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | 15600.00 |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 15500.00 |
| 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | 13200.00 |
| 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | 11400.00 |
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 9600.00 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+-
显示工资最高的员工的名字和工作岗位
mysql> select ename,job,sal from emp where sal=(select max(sal) from emp);
+-------+-----------+---------+
| ename | job | sal |
+-------+-----------+---------+
| KING | PRESIDENT | 5000.00 |
+-------+-----------+---------+-
显示工资高于平均工资的员工信息
mysql> select * from emp where sal>(select avg(sal) mysal from emp);
+--------+-------+-----------+------+---------------------+---------+------+--------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno |
+--------+-------+-----------+------+---------------------+---------+------+--------+
| 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 |
| 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 |
| 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 |
| 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 |
| 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 |
| 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 |
+--------+-------+-----------+------+---------------------+---------+------+--------+-
显示每个部门的平均工资和最高工资
mysql> select deptno,format(avg(sal), 2),max(sal) from emp group by deptno;
+--------+---------------------+----------+
| deptno | format(avg(sal), 2) | max(sal) |
+--------+---------------------+----------+
| 10 | 2,916.67 | 5000.00 |
| 20 | 2,175.00 | 3000.00 |
| 30 | 1,566.67 | 2850.00 |
+--------+---------------------+----------+-
显示平均工资低于2000的部门号和它的平均工资
mysql> select * from (select deptno,avg(sal) myavg from emp group by deptno) tb1 where myavg < 2000;
+--------+-------------+
| deptno | myavg |
+--------+-------------+
| 30 | 1566.666667 |
+--------+-------------+-
显示每种岗位的雇员总数，平均工资
mysql> select job,count(*),format(avg(sal), 2) myavg from emp group by job;
+-----------+----------+----------+
| job | count(*) | myavg |
+-----------+----------+----------+
| ANALYST | 2 | 3,000.00 |
| CLERK | 4 | 1,037.50 |
| MANAGER | 3 | 2,758.33 |
| PRESIDENT | 1 | 5,000.00 |
| SALESMAN | 4 | 1,400.00 |
+-----------+----------+----------+3. 多表查询
顾名思义，就是在多个表中查询，多表又分为两种情况：
-
多表存在着明显的外键联系
-
多表不存在隐藏的外键联系
mysql> select * from emp;
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 |
| 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 |
| 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 |
| 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 |
| 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 |
| 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 |
| 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 |
| 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 |
| 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 |
| 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 |
| 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 |
| 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
mysql> select * from dept;
+--------+------------+----------+
| deptno | dname | loc |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
+--------+------------+----------+
-- 以上就是明显的外键联系 deptno
mysql> select * from salgrade;
+-------+-------+-------+
| grade | losal | hisal |
+-------+-------+-------+
| 1 | 700 | 1200 |
| 2 | 1201 | 1400 |
| 3 | 1401 | 2000 |
| 4 | 2001 | 3000 |
| 5 | 3001 | 9999 |
+-------+-------+-------+
-- 这个表和emp的sal联系，sal在losal~hisal之间决定grade，这种联系比较隐藏- 显示雇员名、雇员工资以及所在部门的名字因为上面的数据来自EMP和DEPT表，因此要联合查询
通过外键联系我们就可以去重。
mysql> select ename,sal,dname from emp,dept where emp.deptno=dept.deptno;
+--------+---------+------------+
| ename | sal | dname |
+--------+---------+------------+
| SMITH | 800.00 | RESEARCH |
| ALLEN | 1600.00 | SALES |
| WARD | 1250.00 | SALES |
| JONES | 2975.00 | RESEARCH |
| MARTIN | 1250.00 | SALES |
| BLAKE | 2850.00 | SALES |
| CLARK | 2450.00 | ACCOUNTING |
| SCOTT | 3000.00 | RESEARCH |
| KING | 5000.00 | ACCOUNTING |
| TURNER | 1500.00 | SALES |
| ADAMS | 1100.00 | RESEARCH |
| JAMES | 950.00 | SALES |
| FORD | 3000.00 | RESEARCH |
| MILLER | 1300.00 | ACCOUNTING |
+--------+---------+------------+- 显示部门号为10的部门名，员工名和工资
mysql> select emp.deptno,dname,ename,sal from emp,dept where emp.deptno=dept.deptno and emp.deptno=10;
+--------+------------+--------+---------+
| deptno | dname | ename | sal |
+--------+------------+--------+---------+
| 10 | ACCOUNTING | CLARK | 2450.00 |
| 10 | ACCOUNTING | KING | 5000.00 |
| 10 | ACCOUNTING | MILLER | 1300.00 |
+--------+------------+--------+---------+- 显示各个员工的姓名，工资，及工资级别
mysql> select emp.ename,emp.sal,salgrade.grade from emp,salgrade where emp.sal between losal and hisal;
+--------+---------+-------+
| ename | sal | grade |
+--------+---------+-------+
| SMITH | 800.00 | 1 |
| ALLEN | 1600.00 | 3 |
| WARD | 1250.00 | 2 |
| JONES | 2975.00 | 4 |
| MARTIN | 1250.00 | 2 |
| BLAKE | 2850.00 | 4 |
| CLARK | 2450.00 | 4 |
| SCOTT | 3000.00 | 4 |
| KING | 5000.00 | 5 |
| TURNER | 1500.00 | 3 |
| ADAMS | 1100.00 | 1 |
| JAMES | 950.00 | 1 |
| FORD | 3000.00 | 4 |
| MILLER | 1300.00 | 2 |
+--------+---------+-------+4. 自连接
自连接是指在同一张表连接查询案例：
-
显示员工FORD的上级领导的编号和姓名（mgr是员工领导的编号--empno）
-
子查询
mysql> select empno,ename from emp where empno=(select mgr from emp where ename='FORD');
+--------+-------+
| empno | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+-
多表查询
mysql> select leader.empno,leader.ename from emp leader,emp worker where leader.empno = worker.mgr and worker.ename='FORD';
+--------+-------+
| empno | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+5. 子查询
又称作为嵌套查询，就是在select语句中再次嵌套select
5.1 单行子查询
指嵌套语句中返回单个子查询结果，如下面问题的deptno
-
显示SMITH同一部门的员工
mysql> select deptno,ename from emp where deptno=(select deptno from emp where ename='SMITH');
+--------+-------+
| deptno | ename |
+--------+-------+
| 20 | SMITH |
| 20 | JONES |
| 20 | SCOTT |
| 20 | ADAMS |
| 20 | FORD |
+--------+-------+5.2 多行子查询
指嵌套语句中返回多个子查询结果
-
in关键字；查询和10号部门的工作岗位相同的雇员的名字，岗位，工资，部门号，但是不包含10自己的
mysql> select ename,job,sal,deptno from emp where job in(select job from emp where deptno=10) and deptno<>10;
+-------+---------+---------+--------+
| ename | job | sal | deptno |
+-------+---------+---------+--------+
| JONES | MANAGER | 2975.00 | 20 |
| BLAKE | MANAGER | 2850.00 | 30 |
| SMITH | CLERK | 800.00 | 20 |
| ADAMS | CLERK | 1100.00 | 20 |
| JAMES | CLERK | 950.00 | 30 |
+-------+---------+---------+--------+- all关键字；显示工资比部门30的所有员工的工资高的员工的姓名、工资和部门号
mysql> select ename,sal,deptno from emp where sal > all(select sal from emp where deptno=30);
+-------+---------+--------+
| ename | sal | deptno |
+-------+---------+--------+
| JONES | 2975.00 | 20 |
| SCOTT | 3000.00 | 20 |
| KING | 5000.00 | 10 |
| FORD | 3000.00 | 20 |
+-------+---------+--------+-
any关键字；显示工资比部门30的任意员工的工资高的员工的姓名、工资和部门号（不包含自己部门的员工）
mysql> select ename,sal,deptno from emp where sal > any(select sal from emp where deptno=30) and deptno<>30;
+--------+---------+--------+
| ename | sal | deptno |
+--------+---------+--------+
| JONES | 2975.00 | 20 |
| CLARK | 2450.00 | 10 |
| SCOTT | 3000.00 | 20 |
| KING | 5000.00 | 10 |
| ADAMS | 1100.00 | 20 |
| FORD | 3000.00 | 20 |
| MILLER | 1300.00 | 10 |
+--------+---------+--------+5.3 多列子查询
查询的条件有多个，返回多列条件
-
查询和SMITH的部门和岗位完全相同的所有雇员，不含SMITH本人
mysql> select * from emp where (deptno,job)=(select deptno,job from emp where ename='SMITH') and ename<>'SMITH';
+--------+-------+-------+------+---------------------+---------+------+--------+
| empno | ename | job | mgr | hiredate | sal | comm | deptno |
+--------+-------+-------+------+---------------------+---------+------+--------+
| 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 |
+--------+-------+-------+------+---------------------+---------+------+--------+5.4 在from子句中使用子查询
子查询语句出现在from子句中。这里要用到数据查询的技巧，把一个子查询当做一个临时表使用
-
显示每个高于自己部门平均工资的员工的姓名、部门、工资、平均工资
mysql> select ename,emp.deptno,sal,tmp.avgsal from emp,(select deptno,avg(sal) avgsal from emp group by deptno) tmp where emp.sal > tmp.avgsal;
+-------+--------+---------+-------------+
| ename | deptno | sal | avgsal |
+-------+--------+---------+-------------+
| JONES | 20 | 2975.00 | 2916.666667 |
| SCOTT | 20 | 3000.00 | 2916.666667 |
| KING | 10 | 5000.00 | 2916.666667 |
| FORD | 20 | 3000.00 | 2916.666667 |
| JONES | 20 | 2975.00 | 2175.000000 |
| BLAKE | 30 | 2850.00 | 2175.000000 |
| CLARK | 10 | 2450.00 | 2175.000000 |
| SCOTT | 20 | 3000.00 | 2175.000000 |
| KING | 10 | 5000.00 | 2175.000000 |
| FORD | 20 | 3000.00 | 2175.000000 |
| ALLEN | 30 | 1600.00 | 1566.666667 |
| JONES | 20 | 2975.00 | 1566.666667 |
| BLAKE | 30 | 2850.00 | 1566.666667 |
| CLARK | 10 | 2450.00 | 1566.666667 |
| SCOTT | 20 | 3000.00 | 1566.666667 |
| KING | 10 | 5000.00 | 1566.666667 |
| FORD | 20 | 3000.00 | 1566.666667 |
+-------+--------+---------+-------------+-
查找每个部门工资最高的人的姓名、工资、部门、最高工资
mysql> select emp.ename,emp.deptno,sal,maxsal from emp,(select deptno,max(sal) maxsal from emp group by deptno) tmp where emp.sal=tmp.maxsal;
+-------+--------+---------+---------+
| ename | deptno | sal | maxsal |
+-------+--------+---------+---------+
| BLAKE | 30 | 2850.00 | 2850.00 |
| SCOTT | 20 | 3000.00 | 3000.00 |
| KING | 10 | 5000.00 | 5000.00 |
| FORD | 20 | 3000.00 | 3000.00 |
+-------+--------+---------+---------+- 显示每个部门的信息（部门名，编号，地址）和人员数量
mysql> select dept.dname,dept.deptno,dept.loc,count(*) from emp,dept where emp.deptno=dept.deptno group by dept.dname,dept.deptno,dept.loc;
+------------+--------+----------+----------+
| dname | deptno | loc | count(*) |
+------------+--------+----------+----------+
| ACCOUNTING | 10 | NEW YORK | 3 |
| RESEARCH | 20 | DALLAS | 5 |
| SALES | 30 | CHICAGO | 6 |
+------------+--------+----------+----------+
mysql> select dept.dname,dept.deptno,dept.loc,tb1.人员数量 from dept,(select deptno,count(*) 人员数量 from emp group by deptno) tb1 where dept.deptno=tb1.deptno;
+------------+--------+----------+--------------+
| dname | deptno | loc | 人员数量 |
+------------+--------+----------+--------------+
| ACCOUNTING | 10 | NEW YORK | 3 |
| RESEARCH | 20 | DALLAS | 5 |
| SALES | 30 | CHICAGO | 6 |
+------------+--------+----------+--------------+6. 合并查询
在实际应用中，为了合并多个select的执行结果，可以使用集合操作符 union，union all
-
union
该操作符用于取得两个结果集的并集。当使用该操作符时，会自动去掉结果集中的重复行。
-
union all
该操作符用于取得两个结果集的并集。当使用该操作符时，不会去掉结果集中的重复行。
7. 表的内外连接
7.1 内连接
当我们使用多表查询时，就是一种内连接，这种内连接有种专门的写法：
select * from tb_1 inner join tb_2 on 连接的条件 and 其他条件-
我们要显示部门名，员工名字，薪水
mysql> select dname,ename,sal from emp inner join dept on emp.deptno=dept.deptno;
+------------+--------+---------+
| dname | ename | sal |
+------------+--------+---------+
| RESEARCH | SMITH | 800.00 |
| SALES | ALLEN | 1600.00 |
| SALES | WARD | 1250.00 |
| RESEARCH | JONES | 2975.00 |
| SALES | MARTIN | 1250.00 |
| SALES | BLAKE | 2850.00 |
| ACCOUNTING | CLARK | 2450.00 |
| RESEARCH | SCOTT | 3000.00 |
| ACCOUNTING | KING | 5000.00 |
| SALES | TURNER | 1500.00 |
| RESEARCH | ADAMS | 1100.00 |
| SALES | JAMES | 950.00 |
| RESEARCH | FORD | 3000.00 |
| ACCOUNTING | MILLER | 1300.00 |
+------------+--------+---------+7.2 外连接
-
左外连接
-
右外连接
这种连接会根据条件匹配一方的条件，如果是左外连接会将左边的表全部展现出来，同理右外连接也是如此。
select * from tb_1 left join tb_2 on 连接条件 and 其他条件我们创建一个学生表stu和一个成绩表cj，具体的情况如下：
mysql> select * from stu;
+------+--------+
| id | name |
+------+--------+
| 1 | 小明 |
| 2 | 小红 |
| 3 | 小刚 |
| 4 | 小华 |
+------+--------+
4 rows in set (0.00 sec)
mysql> select * from cj;
+------+-------+
| id | score |
+------+-------+
| 1 | 26 |
| 2 | 98 |
| 3 | 60 |
| 11 | 68 |
| 20 | 59 |
+------+-------+
5 rows in set (0.00 sec)1. 我们使用左外连接，以id为连接条件，右表会尽可能匹配左表，左表会全部展出
mysql> select * from stu left join cj on stu.id=cj.id;
+------+--------+------+-------+
| id | name | id | score |
+------+--------+------+-------+
| 1 | 小明 | 1 | 26 |
| 2 | 小红 | 2 | 98 |
| 3 | 小刚 | 3 | 60 |
| 4 | 小华 | NULL | NULL |
+------+--------+------+-------+2. 我们使用右外连接，条件同上
mysql> select * from stu right join cj on stu.id=cj.id;
+------+--------+------+-------+
| id | name | id | score |
+------+--------+------+-------+
| 1 | 小明 | 1 | 26 |
| 2 | 小红 | 2 | 98 |
| 3 | 小刚 | 3 | 60 |
| NULL | NULL | 11 | 68 |
| NULL | NULL | 20 | 59 |
+------+--------+------+-------+
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